Tractor mounted plant thinning machine



Ap 7,1953 A. MARIHART TRACTOR MOUNTED PLANT THINNING MACHINE Original Filed Dec. 12, 1944 7 Sheets-Sheet 1 a v wm w my m VM T N T M i A m k M m a \w 3mm T N T. Q w Q n S MN R R mm H l m-Hfmn April 7, 1953 Original Filed Dec. 12, 1944 L. A. MARIHART 2,633,785 TRACTOR MOUNTED PLANT THINNING MACHINE 7 Sheets-Sheet 2 INVENTOR A. Mah'had "fi e, 955244,

ATTORN ELY 7 Sheets-Sheet 3 L. A. MARIHART TRACTOR MOUNTED PLANT THINNING MACHINE ATTOQN EY INVENTOR Zea A Mar/bar) Original Filed Dec. 12, 1944 April 7, 1953 April 7, 1953 L. A, MARIHART TRACTOR MOUNTED PLANT THINNING MACHINE Original Filed Dec. 12, '1944 7 Sheets-Sheet 4 l NVENTOR Zeo 14. Mari/var) ATTO RN EY AP" 7, 1951.".- L. A. MARI-HART 2,633,785

TRACTOR uoumsn PLANT THINNING mourns Originl Filed Dec. 12, 1944 7 Sheets-Sheet e llllllll III ATTORNEY -Ap 7, 1953 L. A. MARIHART TRACTOR MOUNTED PLANT THINNING MACHINE Original Filed Dec. 12, 1944 7 Sheets-Sheet '7 INVENTOR. Lab A. Mari/var) ATTORNEY Patented Apr. 7, 1Q53 TRACTOR MOUNTED. PLANT THINNING MACHINE Leo A. Marihart, Monterey- County, Calif., as-

signor to M. P. H. Industries, Palo Alto, Califi, a corporation of California Original applicationDecember 12, 1944, Serial No.

567,852. Divided and thisapplication'NovemberZ, 1946; SerialNo. 707,438"

4 Claims.

This invention 1 relates generally. to machines. makingmseofa photoelectric or light sensitive;

means forcontrolling agriculturaltools or like operations responsive to light received from.

plants.

In my Patent No. 2A00,5.62., dated .May 21,

1946, thereisadisclosed an agricultural machine making use of a frame adapted'to travel along. a row-.01 1 plants and having ground engaging. cutters or hoeing devicesvcarried by: the frame. and adapted to operate .upon one or more plant rows. The cutters are controlledp'by light sensitive or photoelectric: means: whereby; controlling.v light responses are. secured from. selected: plants in I a desired condition-of: growth. Suchv a machine be-:. arranged: to. perform various functions,

including particularly the. thinning out of plants lie-leave. properly spaced selected plants, and

eradication of weeds as the-desired plants ap-' proach' maturity. A portion. of. the means employed: to control. the. hoeing operations as disclosedinsaidlPatentiNor 2,400,562 consists of a deyice whichcarriesa photoelectric. or. light sensitive: means: inconjunction: withv a source of light which shines upon the plant; caused topass over. the :rowof plants beingoperated upon, and the light sensitive means is sighteduponcertain portions. of the plants to gi v-e a a response indicative of the position 01Ev the root of" thepl'ant. The response thusobtained is-utilized to trip certain mechanismsv for-con.- trolling thehoeing operations.

Itis an object of the present invention to generally improve upon the machine and method disclosed inthe aforesaid Patent No. 2,400,562.

further objector the invention is to. provide a machine of the above character having an improved cycle-of operation and a novel combinationotmeans for carrying out the same. In this connection the invention is characterized by the-feature-that when-used for operations such as the thinningout of plants, a minimum spaci-n'g ismaintained between the plants left standing -but'there is no limitation upon the maximum spacing; Thus 'where the stand of plants secured is relatively poor, the machine does not eradicate good *plantsfor lack of a good plant located within certain intervals, as may be the case with a machine having fixed-limitations.

which is relatively'immune to the effects of exterior---daylight; irrespective of whether or i not This device. is,

2. daylight is excluded from. the plant portionsrflnv der observation.

A further object of the invention. is. to simplify the hoeing .or .cuttingmeans for acting upon the row of plants, particularly to enable fl minar tion of two sets of cutting devices for each row, one for coarse and another for. fine hoeing 011- erations.

Another objector the invention is, to provide. a novel type of machine for carryin out 1196 3-125:

operations on. plant rows, the parts of which are adapted for mounting upon a standard farm.

tractor.

A further. object. ofxthesinvention is to improve upon machines of. the above. character:- with respect to the mechanism utilized tori mounting the various operating parts on atra'ctor, including particularly the supportingg means; for the cutters and the devicesservingto. mount the photoelectric cells.

A-further object of the invention is. to improve upon machines of the above type-:withrespectto the-device or devices which .carry the light sensitive means. In this-connection the present in vention ischaracterizedeby the factthat the aforesaid device or devicesare constructed in such a manner as to be immune tothe eifect of dust.

Another object of the invention is to provide novel means for operating-upon arow of plants to secure the desired light response, andwhich" will bend the plants over in such a manner as to facilitate an accurate light response indicativeof the location of the plants; and for optimum automatic control of machine operations.

A further object of the invention is to provide a device carrying the photoelectric cell which can-be opera-ted under adverse conditions over long periods of time without becoming clogged with the vegetation or dirt.

Another object of'the invention is to providea novel arrangement in conjunction with a photoelectric cell and the source of light, whereby the devicecarrying the photoelectric cell may, be displaced from its optimum path of movement. w-ithoutinterfering with accurate operation oi"v the plant operating cuttersv or hoeing devices.

Further objects of theinvention will appear from the following description in which the pre-.-- ferred: embodiment has been shown in detail in conjunction with the accompanying drawing. :Referri-ng. to the drawing:

Figurexl is a side elevational :viewyillllsliliating.

. a-.machine incorporating the present invention Figure 2 is a plan view of certain working parts of the machine shown in Figure '1.

Figure 3 is a detailed end view showing the construction and operation of the hoeing devices or cutters, and taken on the section line 3-3 of Figure-1.

Figure 4 is a sectional detail showing the releasable clutch for operating the cutters and the timing device, and is taken on the line 44 of Figure 5.

Figure 5 is a section of the same assembly shown in Figure 4, but taken on a plane parallel to the axis of the main drive shaft.

Figure 6 is a sectional detail taken along the line 66 of Figure 5.

Figure 7 is a sectional detail illustrating the control adjustments for the switches of the'timing device.

Figure 8 is a side elevational view, partly in section, showing the device carrying the photoelectric 'cell and source of light.

Figure 9 is a sectional view taken along the line. 99 of FigureB. I

a Figure 10 is a sectional view taken on the line.

Ill-l0 of Figure9. Figure 11 is a sectional detail taken along the line ll-H of Figure 8.

Figure 12 is a side elevational view in section showing a modified form of device for carrying the photoelectric cell.

'Figure 13 is a view similar to Figure 12 but showing-another embodiment of the device for carrying the photoelectric cell.

' Figure 13a. is a side elevational view in section showing another embodiment of a device for carrying the photoelectric cell.

Figure 1317 is a view similar to Figure 13a but showing another embodiment of a device for carrying the photoelectric cell.

Figure 14 is a circuit diagram illustrating oneform of electrical system which can be used with. my machine- I Figure, 15 is another circuit diagram illustrat ing another form of electrical system. Figure 16. is a schematic view illustrating the manner in which the machine operates in plant thinning operations.

Figure 1'7 is a detail showing a modified form of, cutting blade. p

The machine illustrated in Figure 1 has its principal operating parts carried by the frame 'L'Oi a farm tractor A. The balloon tired wheels 8.;of this tractor are driven, and the tractor is steered by turning the single front wheel 9. Such a tractor forms a convenient machine for carryingthe working parts to be presently described, although it will be apparent that other types of tractors can be employed, or a special trailer or motor operated wheel frame can be used where it isnot desired to adapt the machine for mounting on standardized tractors.

A yoke-like frame It] is attached to the forward part of the tractor, and extending from this frame are the frame members I i which can be in the form of structural steel channels. A plurality of brackets 12 are attached to members II as by means of bolts or screws [3, and their positioning can be adjusted laterally as desired. Attached to the brackets l2 by means to be presently described are the two assemblies B, each of which is made up of the operating units B1 and B2. In general the operating units are capable of operating on two adjacent plant rows of a bed and consist of cutters or hoeing devices iii-conjunction with light responsive means for controlling the same. In the detail construction illustrated each of the units consists of the connected frames lea, [4b, which are similar except as to dimensioning. Parallel links l5, [6 have vertically spaced pivotal connections I! to each of these frames, and also vertically spaced connections l8, l9 to the associated bracket 12. Thus the frames Ma or l4b may move in a vertical direction, but are restrained against angular movement with respect to the horizontal. Ground engaging means such as a runner 20 is adjustably attached to one of the frames Ha, 14b (1. e. frame Ma) and serves to support both frames at a fixed distance with respect to the ground level, which distance however may be adjusted to suit varying operating conditions.

The pivotal connection 8 for each pair of links 15 is in the form of a horizontal shaft, to which the links are keyed. In order to provide means for raising all of the operating units in unison, anarm .2l is fixedtoeach shaft, J8, and, is pivotally connectedv with the forwardend Qf a thrust rod 2-2.. At the rear end of the machine, rod, 272

has an operative connection with anarm 2.3..of a suitable operator, such as one of the hydraulic type commonly furnished ontractors. A compression springi l surrounds rod 22,,and its for:

ward end seats uponja. collar 26 which. is fixedto the rod 22, and its rear end seats upon a sliding. block 27.

A rod 28 isattached to block 21 and also connects with an adjustable manual lever 29. By setting the positioning of lever. 29 the tension upon spring 24 can beadjusted, thusiadboth sides of the machine. Adjacent framesfla,

Mb must at all times move together in avertical:

direction because the corresponding linksmli which carry the frames 14a, Mb arekeyed to the. shaft l8.- V.

Each of the operating u nits isv provided. withv hoeing devices or cutters designated generally at 34 and which aredriven by the, shafts 36, through the universal drivecouplings 31. Each shaft 36 is made of telescopically engagedparts which are splined together, whereby the shaft is extensible to accommodate shifts in the relative positioning of the cutters with respect to the frame of the tractor. Each shaft 36 has its rear .end connected through a universal drive coupling 38 to a stud shaft 39. These shafts connectwith. gearing enclosed within the housing: 4!. -The, gearing is driven by a shaft-fl which connects with the tractor power take-off shaft extending fromhousing 53., In general it is desirable that all ofthe shafts 39 and the attached extensible shafts 36 be driven at the same speed and synchronized with the forward movement of the tractor. Also it is desirable that the gearing within the housing 4| be constructed in such a manner that the drive ratios provided can be adjusted to suit varying operating conditions. The two shafts 3B for adjacent units B1, B2 are preferably driven in opposite directions for reasons which will be presently explained. The shafting which serves to carry and operate the cutters includes a tubular shaft 4'6 upon which the cutters are mounted, and an in-,-

Spaced co11ars32, .33 are ,fixed to.

some serves to' house certain parts 'including particularly a cycling clutch by means of which the shaft 46 is rotated by predeterminedangular amounts. i

In order to maintain each box 46 at a fixed. elevation above the ground level along the rowof plants being operatedupoin, suitable means such asthe runners 53 are'pro vided,' and which are adju'stably secured to thefcorrespondin'g boxes" 48. It may be explained in this .conn ection that when the machine is in operation the axes'of the cutter shafts 46 are aligned generally with the rows ofplants being operated -upon. Runners 53am clisposedto engage the'gr'ounol ade ja'cent theplants, while, the runners 23' operate on the plant bed between thefrows of plants, as illustrated in! Figure 3. Therefore, the frames ma, lab will be maintained a distance abov'e the ground level determinedby the contours en gaged by the runners 20, whereas the subframe members 49 will be more accurately located with respect to'the ground level adjacent the-rows of plants being acted upon. p The parts within theboxes-48,(Figurese, 5) include the cycling. clutch 5B, and thetime'r 51. The rear endwall of the boxis provided with a suitable bearing Etfor the shaft 47,. andthe front wallis provi ded'with abearing 59,for.the tubular shaft .46. The; clutch 55 which is interposed be tween-these bearingscan be of the. type disclo ed Patent No. J2A75A32, 1 issued July 5, 1949. Briefly it includes an annular part fit attached to an end part provided with ratchet-like steps or shoulders 62, andwhich aread-apted to be releasbly. e a ed by t e. trigger; rm he. e end of. this arm is urged toward engaged fposition by .ten sionspring Gtandthe armconnects with thereciprocatingoperating rod 65 of -solenoidfifij Associated with an annular memberti there-is a-clutch gripping wire 61-whichqis coiled heli coidallyas illustratedfand which is retained in non-gripping or released position for 'engaged position ofthe trigger lever 63, and while the shaft 41 is..bcing driven in a clockwise direction as viewedin Figure 4.; Immediately upon release of,lever-63.- the wire 157 1001113136 a suflicient amount to grip an inner part,=whichin turn -establishes a drive between the shafts it-and 31. Assuming use. of four. sets of. cutter blades, each release of lever it? causes one-quarter revolution rotation of ithe-shaft 46. In order to insure stoppage of shaft 46 atpredetermined angular positions an annular member 69 is attached to the shaftld-andis-provided with circumferentially spaced peripheral indentations 1|;- Rollerl2 carried by lev'erl3 engagesin these indentations." A tension spring is urges'the roller 'IZtoward engaged position. 1

'While the clutching'means described above is desirable and 'gives'good results, it is to be u'nder'stood 'that other conventionah'types of clutching devices can be used which will afiord 6 cycling operation with relatively accurate predetermined annular turning of the shaft 46;

The timingdevice 5l'can be substantially a s disclosed in-my Patent No; 2,437,168;iissued March 2; 1948. Briefly it consists of a shaft' lfi provided with ajournal bearing 11 to one wall'of the housing. This shaft carries agear '78 which meshes with'a gear-19'fixed to rotate with shaft 31;" Shaftlfi also extends throughand is journaled with respect to a yoke-like bracket 8|, carried by one side wall of the-housing 4&- Between the sides of this bracketthe shaft carries a wheel '82, the periphery of which is friction'ally'engagedtby' a plurality of button-like 'elements 83. These-elements may be small permanent magnets as described in said Patent No.-2,437;168,"or they may be otherwise constructed in order to be'frictionally retained within a trackway formed on the a periphery of wheel82.

Journaledupon thebracket 8! adjacent the wheel :52 there is a star retention wheel 84." R0- tatable with this wheel there is a ratchet wheel Eililengaged 'bypawl 57. Solenoid 38 when energized' serves to disengage pawl tllythus permittingrotation of thestarretention wheel 84 fora sufficient angular distance-to release one ofthe elements 83. Assuming continuous rotation of the wheel 82 the -.-released element 83 rotates tog-ether. with the wheel until it is arrested by its engagement with the series of elements 83 being normally retained stationary by the star wheel.

Suitable switches 9| and 92, such as of the mi'croswitch type, are" provided for actuation by elements 83. wSwitch 9| is shown attached to arm 93, which in turn is: attached to the-worm gear SQ. "la-worm 96-engages'gear 9d, and'is carried by a shaft 91 whichextends to the exterior-of the box ta where it is provided with an adjusting knob '58. Switch 92' is similarly carried by arm 99, which-in'turn is'fixed to gear ill. Worm Hi2 engages gear'-liil,'and :the shaft 163 which carries worm 102 extends to the exterior of the box where it is provided with a similar-adjusting knob we. 'Thus-by turning theknobs 9B and its the positioning of switches 91 and 92 can' be adjusted to any position desired, and as will be presentlyexplained this adjusts the timing of the machine orin other. wordsthe time lapse be tween receipt of alightiresponseby the photo? electric cell andoperation of the cutters. It is desirable that thebox 48be made fluid tig'ht and that it contain" a quantity of *oil, whereby the parts are maintained properly lubricated at'all :v 7' e I;

' As the machine advances: along the plant rows,- each' of-"the shafts t? operates" continuously. E'ach shaft #36 is operatedrecurrently under the control of thephotoelectric means to be presently described, to performfor example thinning or weeding operations wherebysturdy plants ingots condition of growth are left standing at intervals; The cutting means consists of'b-lades' ltti, Iii! grouped in pairs; with the blades being ca'rried by bars'or rods 18,1519, which'in turn'are adjust ably attached to the hubs Hi, H2. The blades are prcvidedwith turned'sharpened edges H3, I l4 which *face toward the direction of" rotation as illustrated in'Fig'ure 3; and'for'thinning oper ations it is desirable to cut away or contour the edges cfthe blades as shown in Fig'uresl and '2; For -operations s'uch as weeding'it isi'de'sirableto use heavier blades illfia', such asshowninFigure 17. The blades I06; ltll'ofeachpair arespaced apartin the directionof travelas illustratedin Figured, and are staggered-one in -iront cit-the other (in directionbf rotationy asillustrated in Figure 3. .{Ihearrangement is such that for a given speed-of movement of the machine, and for a 'give;1 speed of-rotation when the clutch is released, the two blades of each pair will'operate to eradicate plants uponboth sides of a selected plant; The width of the blades is such that their areas of operation overlap for the minimum spacing determined'by the cycle of operation, as will be presently explained. 'For example assuming thatthe minimum spacing is set to be 12 inches, the blades mayeach measure 8 inches in width, with their zones of operation spaced one inch apart, whereby their zones of operation willoverlap for the above mentioned minimum spacing. Itwill be appreciated that the number of pairs of cutting blades may varyin different instances. For example it ispossible-to use two sets of cut-' ting blades spaced 180 apart, in which event the clutch 56, must be constructed in such a manner that when releasedit will cause the shaft 36 to be turned one-half revolution. It is desirable that the, blades be attached to their associated hubs IH, H2 in such a manner as to afiord some adjustment, whereby the machine can be better adapted to ,a variety, of operating conditions. Also itis desirable that the blades be removable for the purpose of "enabling application of blades of difierent sizes and types. Staggering of the blades one'behind the other is desirable in that it tends toavoid clogging between the individual blades of a pair, which would tend to result if these blades were setclosely together. Assuming that the rows of plants are distributed substan? tially as shown in Figure 3, with two rows of plants to a bed and a furrow between the beds, it is desirable that the cutters engage the ground moving. in such a direction as to displace dirt and eradicated plants into the furrows between the beds. It is for this reason that the cutters are operated in'opposite directions of rotation as indicated; V i

The device H6 (Figure 1) consists of a box which houses the photoelectric cell and the source of light. It is carried in advance of the cutters 34 by means enabling individual vertical movement of the same. Thus the sides of the enclosing box are adjustably clamped to the supporting plates II'I, which in turn are attached to the lower ends of the vertically extending rods H8. Each of the rods operates between the roller sets H9 and I'ZI which in turn are journaled to the yoke I22 mounted on member 49. A cross brace I23 between rods H8 is connected to member 19 by spring 524, the tension of which can be adjusted byscrew i25. Thus the device I It is made ireely movable in avertical direction and the weight of the moving parts is counterbalanced to a desired degree by the spring i2 3. By adjusting the tension of spring I213 the device Hi3 may lightly touch the surface or" the ground (as in thinning small plantslike lettuce) or may be retained above the ground'suriace at a desired general operating level (as in'thinning or weeding larger plants such as cotton).

In that form of the invention illustrated in Figures 8 to 11 the device H6 consists of a box 26' which is closed to exclude dust, and which has a glass plate I21 extending over its lower face. Suitable means such as a' soft rubber gasket i28 can'be' employed to seal the plate with respect to the side walls of the box. The plate is removably clamped inplace by side strips I29 whichare releasably attached to the side walls'of tube- 33. The lightfsource is preferably an elon-' gated electric lamp, such as a lamp of the glowdischarge type having a fluorescent coating on its envelope. The photoelectric .tube should have proper-characteristics for the light spectrum employed, and. for example can'be one knownby manufacturers specification as No. PJ-22.

It'can be explained at this point that in operating device 'I Hi the glass plate I27 passes over the plants and the foliage wipes across the lower side ottheplate. It is the function of the photoelectric tube I33 'to secure a lightrespons'e from a plant in a desired condition of growth, and preferably .from a part 'of the plant which is indicative of-the location-oi the central 'axis of the plant root. I have found that light ree spouses from plants are indicative of the central axis of the plant root if the light indication is obtained as reflected light from bent over stem portions of the plant. .By. stem portions 1 have reference to the portions of the plants near'the roots, which in some plants may include some foliage, but which is to be distinguished from the main leafy portion of the plant which spreads out over a considerable area. For accurate indie cation of plant location I limit the area from which a light indication can be secured to a relatively narrow zone, indicated by number I34 in Figure 8, and which extends in. a general lateral direction across the plate I21. It is desirable that this zone be inclined with respect to the direction of movement of the device along the plant row, and that the direction of extent of the zone be generally parallel'to the path taken by the cutting blades as'they pass through the earth. This serves the purpose of enabling some misalignment of each device H6 with respect to its associated row of plants, without however interfering with the accuracy with which the cutters are brought into play to eradicate plants from both sides of the plant from which a lightresponse has been secured.

- With the embodiment of Figures 8 to 11 a narrow strip or response zone is obtained by means which selects reflected light from only a narrow strip or zone and delivers such light to thephotoelectric tube E63. Thus a sheet I36 of suitable transparent material such'as Lucite or glass is interposed between the photoelectric tube 133' and the inner surface of the glass plate l2? as' illustrated. The side edges of this plate are shown convergent toward the tube I33 in order to better collect the reflected light. As viewed in Figure 11 it will be further noted that plate I36 is inclined to the direction of movement at an angle corresponding to the path of movement of the blades through the ground, as previously described. In order to exclude unwanted or extraneous light a suitable opaque shroud I31. is shown about the plate I36 and the photoelectric tube. Also an opaque masking I38 isapplied to the upper surface of plate I21, leaving a strip I39 whichis unmasked, and through which the light may pass. a

7 As iswell known when light passes throughthe glass plate I21, a certain amount of the light is reflected from the upper and lower glass surfaces. The disposition of the light source, the plate I36, and the plate I27, is such that the angle of reflection of light from the surfaces of plate I2! causes such reflected light to be diverted from passing passage of light.

1 7%,... (s red light response. andextraneous lightwhich .1 a re h i we e? a e mm iw S a ;9 upwardly through the plate I36. Light reflected fromfthe upper surface of late I 21 cannot enter ,thelower end of plate I36, and lightreflected from the lower surface of plate 'jIZI leaves this .lower' surface at such an'angle'that it does not pass upwardly. through plate I 36. 'When bent over ste'm portions of "plants passfthr'ough the lre gion' I 34 the angle of 'refle'ction of light from source I32,is such that a considerable part of the light 'reflected froinsuch plant portion passes directly upwardl through plate I36, to actuate the photoelectric tube.

In Figure 8 a' curved frunner I35 "is shown attachedito the box II26 andextending downwardlyfromone rear corner of the same. Such a runner (oi a. s'izeto suit 'soilland" plant .fcondiltions). an be ,ernployed to retain the box at a predet errnined height; above theground level. I

Figur'e'1l2 illustrates a modification of the device I16; In this, instance a second transparent plate "I41, made of suitable material such as Lucite, is interposedl between" the glass plate I 2] andthelight I32. The plate l, 4l together'with f lampfI3z1areprovided withithe opaque shrouding "I42, jwhich canfalsoserve asa reflector. Such an arrangement fservesto niore definitely: distribute a transmit light rom the lamp I32 to, the'zo'ne froinfwhichthe response is. to be made. Here again 'theangular disposm o: the plates 13 s and I41 is suchthat light reflected fr'o'm thef ppe'r and lower" surfacespf plateIZl does not'enter plateI36 to'aiie'ct th'e'photoelectric tube I33.

Figure 131showsjanother arr angernent fot light sourceja'nd photoelectric tube which does not possess -somejof the advantages of Figures 8 to 12 v i'nclusive, butwhichcan be'us'ed in certain instances. In this. instance the box I25 is divided intof conipartments I43; I44 which contain the jlight" 2 and.photoelectric'tub'e I33. A lensf'lflfi d ectl gh ioi 341 1 132 to a ,r triet iance; 1,1. d.. h$.j' l v light reflected frorrr'stem portions of the 1 13 5. i {d i $2. 1 1 the ID1 76- "electric tube iI33."" I-Iere again m'askin'gjj [48715 f us'ed'to' render the greater areaj rtnep ate- I27 opaque; leaving only the adjacent areas I49 and ,I I on opposite sides of the partition lit," for Figures 3a and 'I3billustr'ate further'embodifme'nts of the device jljlfiifl In Figure 131; the wall .,,28I of transparent materialand the box 'fsubstantially' the same as th egglass wall'IZ'! and box) 1'26 of Fi'g'ure}; Within thefh-ox t f e is' a ,Lucite platefor block '283'which'ha's itslower end adjacent'tl'ie inner surface of the iplatelilfan'd l l pr lend adjacent the photoelectric tube 84. Plate 283 is tapered to'wa rdlits upper end he [saine'fgeneral' manner has the plate I 35 illustrated in: Figure 111; A'polaroid screen 235 'is applied to the lowerjend of the plate 283, in

1:52 are .Figure 14 diagrammatically illustrates electrical parts of my machine and the circuit order to eliminate lightdue'to s'tray reflections.

Afl'color lfilter285 isl'interposed' betweenthe upfpe'r end of platelets and'photoelectric tube284. filter imay he one known las Wrattan No.

30, used wi 'tha photoelectric tube of the type known by manufacturers specifications aslNo. .I TZZ-J i i ils ii c n 'fi h m' as previously described, and is enclosedwithin gt e oiia ueln cd or.. s'creen 288. The emb diinentjjust;described [operates substantially, like the ,e nbodirnentof Figure 8v except; that'it fproy-ides aI'rh "re-1'ravombiejrauoitem/sea the light c gji th'ejtube 294 Whichfi'epresents a dereflections, etc.

.ously described devices I I6.

In the embodiment of Figure 131) the transparentiplate 295 has its lower end forming an exterior surface 292 for contactinglthe plant. An extended transparent wall porti on293,' which may be formed either integral with or as a separate part from plate 29L extends below "the source of light 294. f The light source. is enclosed by the hoodor screen 2255. The enclosing box 29? :is provicled with lower allportions 298, Z99, whichf can be formed of suitable metal, and which are suitably sealed with respect to th adjacent edges of. the t al sparent material. It will be, evident that the lower surfaces of walls 295, 295 form 'in effect a'continu'ation of thesurface v 29; 2 f,.in forming a surface or face which is contacted by the" plants.

In both Figures 1311 and 131) the attachment of the box includes side plates llla'whichare connectedjb bar BDLQ A ball and socket asserfnbly 352 serves to attach bar 30I to the rods I I8, Set

screws 3fl31ca'n be loosened topermit tilting of the box to. any desired position Thus'in addition totilting the box asshovvn in Figures 13a, 13b, a. side tilt can be provided; which may. be

vdesirableivi'herefth'e plants are not growing perpendicular to the ground level. I

Devices I I5, 282 or-ZS'I may hayetheposition- .ing, of the; phototube'lamp and associated Parts displaced by or. arrangements ,rsuch as shownuin {Figures 8 to 13 or l igure 13a can be reversed end for end (i. e.: turned thr'oughi 180 assuming that the runneris; properly :repositioned on they-rear end of;lthe same. I various connections which can be. used for thesame. .The

photoelectrictube I33, of each device -I I6 is con,

nectedto an'amp1ifier 'l53 of theelectronic type, whichin turn may connect to the input of a secondamplifier 1 54; Relay I55 has one winding -I55 of the same connected to the output-of amplifier I54 and is shown provided. with two sets ofv contacts 151,458 C0ntactsI5'I control a cir- .,cuit,whi ch includes condenser, I59 (one Side'Of which is grounded),'contacts I51, and the'solenoid 88:0f theitimingdevice 51.. Upon closing the 'contactsqlfl condenser I59 is discharged throughwinding sfl to release one of. the elemerits '83. When contacts I51 are opened condenser IE9 is charged by a charging voltageapplied to the same throughzthe resistor I6I.- Contacts I58-contro1 a circuit which can be trac'e'd fromthese contactsthrough a second-"winding I62 for the relay I55, a source or current represented'by battery I63, and microswitch lil back to the contacts I58. The contacts of microswitch 9i are normally closed but are opened'by passagefof one of the element's fitinfproxirnity to the same; Another circuit is provided'which can be tracedfrom the microswitch 9 2 "through the. solenoid f'fifi "for releasing the clutchf56yfa source of current represented Jby'the battery -I 6 4,

ft'h' syste back to the switch 92. The contacts 92 are normally open.

, The cutting devices 34, the clutch E, and the timer- 5'! "arediagrammatically indicated as being driven from a common shaft I65, which is reprei'sentative of the motor shaft of the vehicle.

i It;is, desirable that the lamp I32 provide a pulsating source of light, and that the'amplifier .l53 be of the alternating current type tuned to "res ond to the same freqency. For example, as-

suming that lamp I32 is of the fluorescent'type, it .can be excited with alternating or pulsating current ata regular frequency of say 115 cycles, whereby-the light from the lamp has a frequency of 230 cycles. Amplifier 153 can be tuned to respond to theesame f r.eque,ncy, and amplifier 154 can be made to provid'e'a' direct current output forproper operation of the relay 4 5%. The ad- "lvantage of suchan arrangement is that the machine-is made immune to extraneous light which is .not pulsated. at the frequency for which. the apparatus is responsive, and therefore no pre caution need be taken to exclude daylight. Assuminghowever that one desires to use a constant source of light with an untuned amplifier, then daylight should be excluded from the lower side of the plate [21, as for example by providing suitable-opaque flaps orcurtains along the sides, front and back of the device l 16. p I

pjerationfof the system shownin Figure 14 is asffollowsf'Assuming that. a light indication of properirequency is obtained by. the photoelectric tube 133, electrical pulses of .proper frequency operate the amplifier I53, and as a result amplifierflfitsupplies current to the winding I55 of relay (56 to close the contacts or the same. Condenser l59 is thereupon discharged through contacts I51 and the solenoid 88, to release one of the elements 83 of the timer 57. At this time it is that the wheel of the timeris being operated continuously inconjunction with" advance or the machine along a row of plants; and thereiore thereleased element travels with the wheel toward the switches '9 I 92. At the same time the contactslSlare'closed the" contacts l 58 are closed to "provide a holding'current from a battery E53 'through'thejwinding l62 of the relay. -When the released eleme nt 83 reaches the microswitch 9! "the contacts of' this switch are momentarily of "switch "opened'with the result that the holding circuit 1 isiinterrupted to permit the relay W6 to open both contacts l5] and I58. During thetime the "'c'ontacts'jfil and IE8 are retained closed, the relayjs made iinmune with respect to further impulses. However after being released'by operation-of-switch 9|, the system is in condition to receive a new impulse from any one plant of the row'bein'g operated upon. As the released element proceeds to operate the microswitch 92, the energizing circuit for the solenoid 66 ismomen- 'tarily closed to release'the clutch 56. This :causes cyelicmperationwe theiiouttersiefi 4i touturnsthe A pie "t'e altliat mm the-ifiiniiiiiilm left standing in the tithe-ugh it''uoes' limit or determine them'aximiirnf'spacingj The maximum spacing'is-de'termined by thefreqiiency with which good. plants are encountered: inffthe row being operated upon, assuming that the device is '50 adjusted that a plant must b'e s u .y and in good condition to provide a propejr re fiecting surface for securing- .a, desired response. The time delay is also desirable in that 'it permits location of the photoelectrictube-.aheadfof the. cutters,-Whe1 e it is not affected by fragments ofsoil and foliage thrown 'to one side .as the cutters pass through the ground. V

In place of the arrangement of Figurejjlgl it is desirable to makeiuselofgth ele trica gsystem disclosed and claimed 'inapplication Serial Number. 707,510,- filed NOVembe'r-Z; 194$, now Patent No. 2,596,591 dated May, 13,, 1952, which is illustratedin Figure 15. This system includesthe device lfifi whi'ch h'ouses'the light source" 167 and the photoelectric cell "568. The light source is a fluorescent tube excited from alternating current supplied by the transformerlefl, which in turn has its primarysupplied with pulsatingv current from the vibrator ,!.'l. A suitablebattery .172 can be-provided io'rfoperating the vibrator ill, in a manner known to those skilled in the art. Tube It! can be of the type provided with a suitable starting circuitunder-the control of startingswitchllZ. f

The terminals of photoelectric tube IE8 connect withauip'liiying means including the cascade connected vacuum tubes H6 and 111/ The particular tubes illustrated'are of the triplev grid amplifier type, such as tubes known by manufacturers specifications as. No. SSJ'Z. Resistance coupling is provided between the photoelectric tube andthe input-of tube 175.. Conductor H8 is connected to one sideof photoelectrictube F58, and is grounded. Conductor I19 ,c'onnect'sthe other side of the photoelectric tube (the anode) to the grid I82; in series with the coupling. condenser 184. Coupling resistor. i85 connectsacross conductors H8, i'l's andfa'leak resistor I81 "eonnects bteween conductor l'l8and, the grid I82. The cathode lii'qandgridlfll areconnected'to ground throughthe biasingresistor 188, The anode 139 of tube IE6 is connectedin-series with the resistor E9! to the conductor 192," which in turn is connected to a' source of plate'supply Voltage thro'ugh'the resistor I93. In a typical instance the voltage of the plate supply can be of the order of 350 volts. Conductor Hi2 connects to ground through the series connected voltage regulating tubes I9 5, I95. These tubes. can be of the type known by manufacturers specifications as VRlfiG. The voltage is applied to anode of the tubelEB by means of the resistors I and 91, which function as a filter in conjunction with condenser, I98, and as a voltage divider in conjunction with resistor H36.

The second grid I99 of tube H6 is connected to snoundthrou h. the. ot-pass;iccndensexis lisan islalsoiiccnnected.itonconductor olazctlmm aheib icsiston 2&2,. wherebxiaasuitablervol icediiiscnithee iida 'iiheracuum heiit'ijh si t 11o an -aldjnstabletan; onzhesistnnifiia :"bonnected ;-to

through the rserlesicoupling nondehser 2235 .fjustin"g.the setting of.-.=the.:tap;on :resisto: 2 'cas'a sensitivity adliiistmentcI" Theggrid'fzfli ube IT! connects with th'ehath'ode :20Bgrhndatlfehce ridT'ZI I :resis tor 266. -is normally open, hasits one side grounded and'its .other side connected by, conductor 20'! to.;the staztionary contact 40f the relay; In additionthis conductor is 'connected to one sideofqa'jsimple "push; buttQn Or switch 253, the other side of which;is grounded. Switch, 92 hasitsone side rounded and its other side connected byconducfdenser 2l0, and to the conductor I92 through the resistor 2!2,7 wherebya suitable voltage is maintained: upon the'grid withrespect to the potential maintainedon-thecathode. The plate 2l3 of tube IT! is connected to the conductor I92 through a suitable tuned circuit 214 consisting'for eaxmple ofthe inductanceZIB and shunt capacitance .2; This circuit is tuned toithe frequency of the light source whereby-theamplifying system is responsive onlyto pulsations of substantially the same frequency.

Condenser 2!8 servesto couple the plate 2l3 of tube l1! tothe grid 2l9of-anothervacuum vtube 22!. 'type such as a three element-tube known. by :manufacturers specificationsvas No, 884, or a This tubecan be of the thyratron tube of the shielded grid typeknown as'No.,2050.

,TheIcathode; 222 of thyratron 22!. is grounded .as indicated, and the grid is connected to. suitablesource of negative bias through theseries ;res istors 223, 224.. Condensers 226, 22! are shown connected from the negative bias to,ground,- and from-the mid connectionbetween resistors 223,

224 andground. M v I v 3 H In conjunction withthe thyratron 22! there is a relay,228 provided withtwo sets of contacts-l, 2. and 3,;4.; Thestationary contact 2 connects 1to;-the plate 229 of thyratron 22!; Thecooperating movable contact I is connected by conductor 23! andJthe series. resistor 232 to the grid 233 of another vacuum tube 234. This tube-can be, of the.'triode-amplifier type suchasa tube known by. .manufacturers specifications as No.

6J5. The plate 236 of thistube is connectedby conductor 23'! to a suitablesource ofplatebat- .tery :potential, .such as potential of the. order of 250 volts. Thecathodei 230 is connected by conductor 239 to-one terminal of the coil 24! of .relay 228., :The othersideof this coil connects .to the stationary contact 4. Grid 233 is'also con nected to ground through the leakresistor242.

The'release-coil 88 f the timer hasvits one terminal connected by conductor 262 tothe coniductor 23!, and. thus: to the movablecontact, l, and. its other terminal connected; by: conductor 1 i 263 toone side of a current supply condenser264,

the-other side of which is grounded. Conductor 263 also connects to conductor 237Tthrough1the Switch 2!, which vin this instance tor 263 to one terminal of the. clutch release solenoid-66. The other side of thissolenoid isconnected bycOnductorf 2"!! to the conductor 23'! :and" to the plate current supply'lofv tube 234- through the series resistor 272. Also conductor 2]! is connected to onesidevof thecurrent su ply condenser 273, the other side of which is gro n v M I v.

A small signal or 'indicator 'lamp 2?G' of the neon or glow discharge type is shown connected between conductor263 and the'groundQin series with a resistor 217; i I

Assuming operation'at the same frequency'as 'me'ntioned; in connection with Figure l hnameiy 230'cycles per second, the various-: resistors and condensers included in the network may i have value'sas*iollows:' Resistors H36; !8'!;'-}!3'B and Hi, '2'-megohms; resistor 183;:12000hm's; resistor Hi3, zscu'ohms; condenserl98, ZO'fnfdJ: resistor !9!,

one of the elements 83; denser 264as described causes the lamp 276 ,to beextinguished Simultaneously with 264 the potential of conductor-Hi and grid 233 of tube 234 is reduced from a relatively high positive value of the order of say200 volts, to a relatively lowpvalue- This serves to block the plate current of tube 234, or inotherword s topro- .vide a relatively high plate to cathode impedance.

14 220,000 ohms; condensers I84 and'206, 0.01 mfd.; condenser 20!, 20 mfd.; resistors 202 and 204,1 megohm; resistor 209, 500 ohms; condenser :2!0 20 mfd,; resistor 2I2,150,000 ohms; resistor 223, 100,000 ohms; resistor 224, 10,000 ohms; ,condenser226,v 0.25 m fd.;.condenser 221, 0.025 mfd; condenser 2.!8,'.0.01.mfd.; condenser 204, 20 mfd.;

resistor 266, 5,000 ohms; resistor 212, 5,000 ohms; resistor 232, 150,000 ohms;'resistor 242, 200,000

ohms; condenser 213,130 mid; and resistor 21?,

100,000 ohms.

Operation of the electrical system shown; in

Figure l51is as follows: Lamp ii! is started in operation by: closing the switch H3. Switch 268 is then momentarily and manually closed to energize coil 24! by current supplied fromthe cathode of the tube 234. Closing of, the contacts of this relay; causes the relay to. belocked closed because the closing of contacts 3 and 4- completes the holding, circuit to ground through. the coil 24!. The grid 2.!5 of the thyratron 22lis biased at this time in such manner that the. plate to cathode impedance is relatively high. Thev plate current sourcev connected to conductor 23'! charges condenser 204 through resistor 266,.and also charges condenser 213,throughresistor2'i2.

AS long as condenser264 .is charged the small neon indicator lamp 216 is'illuminated, Assuming nowthatj a plant passes beneath the plate I21, it causes a refiectedlight indication to fall upon, the photoelectric tube. I68, whereby pulses of a. frequency corresponding to the frequency :of thelight are applied to the input of, thel amplifier ,tube, ;!'!6, and amplified I pulses are impressed upon the input of the amplifier tube H1.

The amplification system isresponsive only to pulsestoi the light frequency'because of the actionof theresonant circuit 2l4. Whenthe tube ll! receives amplified pulses plate 2E3 assumes a potentialjdiffering'from the potential of the 'thyratron grid 2!9,"and therefore-the potential of the thyratron gridis changed whereby the thyratron is fired, or inother words the plateto "cathode impedance reduced to arelativelylow ;,value.. When this occursthe condenser264 discharges-through a circuit including the timer coil 88,.relay contacts! and 2, and the plate-to cathode path of the thyratron, to efiect; release of the starwheel of the timer to therebyrelease Dischargev of the .con-

discharge. of condenser As a result flow of holding current through the .relay coil 2 is interrupted or reducedto a relatively low value,- whereby the contacts of the relay are released. Release of the relay rendersthe networkw incperativeinsofar as iurther pulses from the photoelectric cell I60, are concerned.

"Upon release of the relay-22fijthe' openingof {contacts 1 and -2 .p ermits the grid233 of tube 234 to 'againassume, a relatively high-positive. value, with 'the result that the plate to cathode im- '70 When the released element 83has traveled suflipedance of this tube is again made-relatively, low.

ciently 'far to operate the switch 9 I closing of this' switch establishes a currentflow through coil 1 24! of the relaygwith the result that the relay is again/closed to cause the apparatus to :be conditionjeidp'to receiveancth'er light response; When the released element reaches and'o'perates the switch 92, a circuit is closed which includes coil 69 and the condenser 2'33; whereby thi's c'ondenser discharges through the coil 66 to release the clutch 56. Release of this clutch permits the cyclic operation of thecuttersfM-to perform a thinning operation-as previouslydescribed. Immediately upon discharge of condensers 264 and 213 in the manners described above they are recharged by current supplied from the plate current supply connected'to conductor 231.

The electronic network of Figure 15 and the controls for the same can be housed within a suitable box 25 (Figure 1). The controls provided for the operator on the panel of this box include the pilot light for each unit, and also a sensitivity control for each unit formed by a potentiometer representing the resistor 204 of Figure 15.

An explanation of Figure 16 will assist in understanding complete operation of the machine. Ihe simplified diagrammatic elements indicated in. thisfigure representthe elements of like numbering of themachine. Ihe putting blades 166-, are indicated as engaging the ground while moving outwardly of the bed and toward the adjacent furrowsand also moving forwardly with the general movement of the ma chine frame. In cutting through the row of plants they eradicate plants in front of and behindfla selected-plant, over a predetermined interval. The extent of operation of each set of cutting blades is preferably made such that it is substantially greater than the minimum spacing determined by the timing device, as previously described, and somewhat greater than the normal expected spacing between plants left standing. Assuming that the machine is being used for thinning operations on plants like lettuce, the blades can be proportioned so that each set cuts over a length (in the direction of movement of the machine) of about 16 inches, and the timing device set so that the minimum spacingbetween plants left after the thinning operation is about 12 inches. -The devices photoelectric cells pass in wiping engagement with the young plants, tilted at an angle such as illustrated in Figure 8. With plants like lettuce the counterbalancing of each device can be such that the rear edge of the glass plate l2! rides lightly upon-the ground surface (or a short runner 135 can be employed), whereby the plants of proper growth are bent over to expose bent over stem portions as they are received in the response zone-134. When a sturdy stem portion is received in the zone 534, that is the stem portion of a sturdy plant in such proper condition as to permit the same to stand, a, light response is obtained from the photoelectric tube and as the result-the solenoid of the clutch 56 is tripped to activate the cutters I66, I07, there being a sufiidierit tithed nay aspievieusiy eeseriseu whreby tfi cilttsrs efe arugiieinte fias te ete awas;an newss and-" ausa pie 'frofii" whren tue resha e assua e rested drj'dg'i aifiiiiatically -1 Figure ldtlie plants l'eit stari'dingbiiig ifidiatefi by dtcrossd@lrclfi @He ie'sultant pa h df *ni'ovn'ient or the {cutters thic'iuglithe gr n denser-a seretea pianei substa ii'tially-pa'rall'l tb weeene'suo m rleane Figure lfirillustrates-how for'a: reasonablyv -good (-15 tense strum rhe -axis:- (liiz i ta H6 which carry the Q16 standof plants, theplants left standing will-all be at or near the minimumspacing. However when the stander plants is'poor, as may occur at certain points along the row, the spacing may be as much as two feet or more between the plants left standing.

The above will make clear the primary. features of the invention. It will be evident'that the fields in which my machine i to be utilized should be sown in accurately spaced rows, with the rows as straight as possible. When the seeds have: germinated and the plants reach a proper size for thinning, my machine is employed to take the place of the usual hand thinning operations. The machine is first lined up with the row of plants upon which it is to be' operated, andthe frames 49 are lowered until the skids or runners 2i! and 53 engage the ground. The depth to which the cutters operate is dependent upon the adjustment of the runners 53, and upon the adiustment of the blade themselves with respect to their associated hubs. When at rest the cutters I65, I07 assume an angular position in which the cutting blades clear the ground. However when actuated by releaseof clutch 56 the cutting blades rotate one-quarter of a revolution and as previously described during such rotation two blades pass through the ground in front of and behind the selected plant to eradicate the plants which are not desired. It will be evident that in some instances where the stand is relatively close, more than one plant will be left standing between the zones of operation of the blades. However such groups can be readily thinned out by a simple manual clean-up operation. Also it i evident that where the stand is relatively poor and where the selected plants left standing are spaced relatively far apart, some poor plants may be left standing between the good selected plants. Such poor plants can be readily removed by a manual clean-up operation-a 7 It will be evident that the machine is capable of various set-ups for diiferentltypes of plants, and for diiierent types 0f operations desired upon plant rows. For thinning operations the machine can be used to advantage with a wide variety of plants, including lettuce, cabbage, cotton, broccoli, sugar beets, and radish. After the plants have been thinned and have reached a fairdegree of maturity thernachine canbe utilized to advantage for Weeding operations to eradicate undesired weeds between the plants. For weeding operations it may be desirable to introduce suitable color filters in conjunction with the source of light or the hotoelectric tube, or both,'in order to provide for proper color discrimination between the desired plants and the weeds.

In operating upon plants, such as cotton, which are relatively sturdy and are not planted closely, the devices 11 6 canbe adjusted (by use of a run- .ngitii iii r e tf ei ilv' .1 9 agree spear. at .v a. a. i a n v. mug? g aaeaet fep'g i slam ee sea et.

be made to. suitthe ma saneie s seihaiil e i llt llieth 19%.

pa e @941 eBszl, iB-finiifinc a l... W t -commeuatmarheimachiaeimplants entnistancesiapart. the adjusted fiwit 'l respec l7. chine to different soil conditions and different types of plants.

As has been pointed out in connection with the description of various types of devices for carrying the photoelectric tube, the box or mounting for these devices can be tilted to different angles in connection with adjusting the vertical positioning of the same above the ground level. Combined adjustments of this type serve to best adapt the machine to different size plants, and particularly serve to vary the size of the plant which the photoelectric tube must view in order to trip the clutch. Thus by proper adjustment of the general elevation of the device I I6 and by tilting the same to a suitable angle, it is possible todiscriminate against poor undersized plants (such as lettuce plants being thinned) and to select only sturdy plants which are equal to a minimum size requirement. r

My machine is not affected by severe dust conditions. This is because the glass plates I21 are being continuously wiped by the plants, and therefore they are kept sufiiciently clean at all times for transmitting light. In addition responses are obtained from portions of plants which contact or are in relatively close proximity with the lower surface of the plates I21, where the plant portions can be viewed relatively-clearly. In other words the intensity of the light response is critical with respect to the distance of the foliage from the-surface of the transparent material and falls off at a disproportionate rate as the spacing is increased. This characteristic increases the accuracy of the response and aids in discriminating against light reflected from extraneous surfaces, such as the surface of the ground. It has been found that the plate I2! will be kept wiped clear of dust irrespective of various climatic, dust or plant conditions. Moisture or dew upon the plants will not cause serious incrustation or accumulation of films of dirt or dust, and the same is likewise free of oils or plant juices commonly found upon plant leaves. In general as the devices IIB pass over the plants of the row the plants are viewed commencing with the root and traveling towards the leaves. This insures a light response from a portion of a sturdy plant which is relatively close to and indicative of the central vertical axis of the plant root. Thus in operating upon plants such as lettuce it has been found that when a sturdy plant is viewed it is only necessary for a small length of the bent over stem to appear in view in the zone I34, in order to secure a desired response. The plants are not damaged by passing under the devices H6 or below the rear edges of the plate I21. The upper sides of the glass plates and also the photoelectric tube and light source, being entirely enclosed, are not affected by dust or moisture conditions The edge contouring of the blades I06, I01 is desirable in that it tends to prevent a windrow effect at the ends of edges H3, H4, which tends to drag soil across the selected plant with possible covering of the same. However as previously mentioned, heavier blades may be preferred for weeding and like operations.

In the foregoing it has been presumed in describing operation of the machine that the plants are grown in raised beds, with two rows to the bed, and with furrows between the parallel beds. In some instances however it is not customary or desirable to cultivate the plants in this manner. It will be evident that my machine can be adjusted for use with other types of agricultural 18 methods as for example where the plant is grown on fiat ground without intervening furrows.

Certain features of my invention have application to a variety of argricultural machines, including for example machines for harvesting plants or products, or for controlled application of sprays or fertilizer to plants.

This application is a division of subject matter disclosed and claimed in my copending application Serial No. 567,852, filed December 12, 1944, now Patent No. 2,502,468, dated April 4, 1950, and entitled "Agricultural Machine and Apparatus.

I claim:

1. In an agricultural machine of the type described, a frame adapted to move along a row of plants, a secondary frame carried by the main frame, means enabling elevation or lowering of said secondary frame to a desired position, hoeing means adapted to operate upon the row of plants, means forming an attachment between the hoeing means and said secondary frame to enable vertical movements of said hoeing means with respect to the ground level, a ground engaging member contacting the ground adjacent the plant row and serving to maintain said hoeing means at a generally fixed elevation with respect to the adjacent ground level, irrespective of the vertical positioning of the main frame, a device including a photoelectric tube disposed in advance of the hoeing means and adapted to be moved in close proximity with the row of plants, means serving to carry said device from said secondary frame enabling free vertical movement of said device relative to both the secondary frame and said hoeing means, and means enabling automatic control of said hoeing means by said photoelectric tube.

2. In a machine of the character described having a frame adapted to be traversed along a row of plants and a device including a photoelectric tube carried by the frame and adapted to pass in close proximity with the plants, the photoelectric tube serving to receive light reflected from portions of plants, hoeing means carried by the frame and adapted to operate upon the row of plants, and power means for operating the hoeing means whereby the resultant path of movement of the hoeing means through the ground as the machine moves forwardly is at an angle to a plane normal to the path of movement of the vehicle, said hoeing means being controlled by the photoelectric tube the improvement comprising mounting means for said tube and light transmitting means carried by said mounting means and interposed between the tube and said plants, said light transmitting means serving to transmit light from a confined relatively narrow zone disposed parallel to the resultant path of movement of the hoeing means.

3. In a machine of the character described, a frame adapted to be traversed along a row of plants, rotary plant hoeing means carried by the frame and adapted to operate upon the row of plants and including at least one pair of cutting blades disposed to cut in front of and behind a se-- lected plant, power means for driving said hoeing means, each of said cutting blades having a blade length measured longitudinally of the row of plants which is less than the minimum spacing to be left between plants, a light source carried by the frame and serving to illuminate the plants of a row, photoelectric means in advance of the hoeing means and carried by the frame in position to move in proximity with a row of plants,

responses from plants in good condition and in advance of cutting operations upon the row, means serving to control operation of said hoeing means responsive to receipt of a light response by said photoelectric means, said means including means for interposing a predetermined time interval delay between the receipt of a light response and the operation of said hoeing means, and means serving to prevent operation of said hoeing means by receipt of a second light'response Within a predetermined period of'time following receipt of one operating response,.said last means serving as mean providing a predetermined minimum spacing between good plants left standing, said minimum spacing being greater than the cutting length of each of said cutters.

4.- In a machine of the character described, a frame adapted to move along a row of plants, rotary hoeing means adapted to operate upon the row of plants, said hoeing means including at least one pair of cutting blades disposed to pass in front of and behind a selected plant when the hoeing means is rotated, each of said blades having a cutting length as measured in the direction of travel of the machine which is less than the minimum distance desired between plants, a source of lightcarried by the frame and serving to illuminate the plants of a row, a device including a photoelectric tube adapted to receive light responses from plants located in advance of said hoeing means, power means for operating said hoeing means, means for controllingiapplicati'on of power to said hoeing means in responselto :the receipt of light responses by the photoelectric tube, said means including means for interposing a pre-1 determined time delay between the receipt of "a by the photoelectric tube for a predetermined time interval after the'receiptof an operating response, said last means serving as means to provide" a predetermined minimum spacing between the plants 'leftstanding which-is greater than safd'cutting length.

REFERENCES err-E1) The following references are of record in the file of this patent: I I

UNITED STATES PATENTS 'LEO'A. MARIHART. 

